Beer Fact Friday: Cooling
Welcome back to our overview of each step of the brewing process, folks. So far, we’ve MILLED our malted grain, MASHED it with hot water, LAUTERED the mixture to separate the liquid wort from the spent grain, BOILED the wort, and WHIRLPOOLED the liquid to remove protein and hop matter. Whew. The wort is almost ready to be fermented, but at this point it’s still hot. Before it can be placed inside the tanks, we need to cool it off.
There are a few methods to accomplish this. The first is through use of a coolship: A large, shallow, open vat that’s sort of like a beer bathtub. Coolships bring down the temperature of wort by exposing as much of the liquid to cool air as possible, but they come with their own set of problems. Exposure to open air increases the chances of spoiler bacteria getting inside the wort and contributing sour or funky flavors—not great unless you’re brewing wild ale. As such, coolships aren’t used much for cooling wort in modern breweries.
The more common cooling device is known as a “heat exchanger” or “plate heat exchanger.” These are metal instruments that range in size and consist of a series of plates through which liquid can run. Hot liquid (in this case, our hot wort) flows along one side of the plate while cold liquid (usually water or glycol) flows along the other. The wort becomes cool enough to ferment, and the cold water is heated and returned to a hot water tank, ready to be used in the next batch. Heat exchangers are usually sized to cool the entire contents of the kettle in less than an hour.
Why is speed important? An off-flavor called dimethyl sulfide (DMS for short) develops when wort is hot, but not boiling. The more time it spends at a high temperature, the more DMS—which tastes like creamed corn—will end up in the finished beer. So brewers are incentivized to drop the temperature of the wort as quickly as possible.
Once the wort’s cooled off, it’s ready for the fermentation tank. We’ll cover that stage of the brewing process next week.
Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on Facebook, Instagram, or Twitter—for more fascinating beer trivia.